1. Field of the Invention
The invention pertains to the field of variable cam timing systems. More particularly, the invention pertains venting of the variable cam timing phaser or mechanism to enhance warming of a variable cam timing phaser.
2. Description of Related Art
During engine startup, when an engine is cold and the oil viscosity is high there is a delay in getting warm engine oil to flow through the variable cam timing (VCT) mechanism, and therefore delays occur in obtaining the increased performance of the VCT mechanism when hot oil is available. Since the VCT mechanism is a hydraulic mechanism that uses engine oil as its working fluid, the performance of the VCT mechanism is reduced at a higher oil viscosity. Therefore, it is desirable to introduce warm oil to the VCT mechanism as soon as possible to increase the VCT mechanism's performance.
Most prior art VCT mechanisms are designed to limit oil consumption when the engine oil is hot and at low viscosities. This same design limitation also limits the exchange of oil in the phaser at low oil temperatures and higher viscosities. The low exchange rate of oil in a typical VCT therefore limits the rate at which warmer oil is introduced to the VCT during the engine warm up cycle.
This design delays getting warm engine oil to flow through the VCT mechanism and therefore delays the increased performance the VCT mechanism experiences using hot oil. The VCT mechanism's performance can affect cold start emission and cold engine drivability so it is desirable to introduce warm oil into the VCT mechanism as soon as possible.